NSFGEO-NERC: Quantifying evolution of magmatism and serpentinisation during the onset of seafloor spreading

这是一个由国家科学基金会地球科学理事会（NSF/GEO）和联合王国国家环境研究理事会（NERC）通过NSF/GEO-NERC牵头机构协议共同资助的项目。该协议允许美国/英国提交一份联合提案，并由研究者拥有最大预算比例的机构进行同行评审。一旦成功地共同确定了一个奖项，每个机构就为预算的一部分和与其自己的调查人员和工作组成部分有关的调查人员提供资金。当大陆分裂和裂开时，海洋盆地就形成了，允许下面的地幔岩在大陆边缘之间上升，融化，形成新的海洋地壳。 当有大量熔融时，这一过程看起来像是洋中脊洋壳的形成。 然而，在一些岩浆贫乏的边缘，大陆地壳因断层作用而伸展和变薄，并允许地幔在地壳下上升，并暴露于沿断层渗透的水。 地幔与水结合形成一种叫做蛇纹岩的岩石，富含水化滑石矿物和磁铁矿，磁铁矿是一种磁性和导电矿物。加深对大陆裂谷过程的了解是重要的，但最常用的地球物理工具地震方法很难区分下地壳岩石和蛇纹化地幔。 电磁（EM）地球物理方法可以对地壳和地幔的电导率进行成像，该项目将结合使用地震方法和EM方法来研究英国西南部的岩浆贫乏边缘。 从这个更好地了解基本的构造，化学和大陆裂解的热历史将获得。 热历史对该区油气的生成具有重要意义，大陆的裂解涉及伸展构造和岩浆作用的复杂相互作用。这一过程的最后阶段导致海底扩张的开始，人们对这一阶段的了解仍然很少。一个共同的端元包括超伸展大陆地壳和广泛的地区的折返和蛇纹状（水合）地幔。大洋中脊、裂谷边缘和俯冲带的蛇纹石化作用介导了岩石圈和水圈之间的地球化学交换。有证据表明，正断层在供应流体驱动蛇纹岩化超伸展大陆地壳下，可能在地区的折返地幔中起着关键作用。然而，镁铁质地壳岩石和蛇纹化地幔岩石的地震P波速度是相似的，因此地震资料的解释是不确定的。蛇纹石化地幔岩通常比镁铁质地壳岩石导电性更高，通常约一个数量级，因此受控源电磁（CSEM）和大地电磁（MT）技术为解决岩石圈结构争议提供了一条有前途的途径。 该项目将侧重于缺乏岩浆的戈班支脉裂谷边缘，以便㈠沿着两个精心挑选的断面获取高质量的同步可控扫描电镜、大地电磁和广角地震数据集; ㈡利用这些数据获取岩石圈上部几公里的同步高分辨率地震速度和电阻率模型，以及几十公里深处的低分辨率模型; ㈢解释由此产生的模型，以量化地幔蛇纹化和岩浆增加的区域和局部变化;（iv）将这些观测结果与岩石圈伸展、地幔水化该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准。

This is a project that is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own ivestigators and component of the work.Ocean basins form when continents break up and rift apart, allowing mantle rock beneath to rise up between the continental margins, melt, and form new oceanic crust. When there is abundant melting, this process looks like the formation of oceanic crust at mid-ocean ridges. However, in some magma poor margins, the continental crust stretches and thins by faulting and allows mantle to rise beneath the crust and be exposed to water penetrating down faults. Combined with water, mantle forms a rock called serpentinite, rich in hydrated talc minerals and magnetite, a magnetic and electrically conductive mineral. It is important to understand more about the process of continental rifting but the seismic method, the most commonly used geophysical tool, has trouble differentiating between lower crustal rocks and serpentinized mantle. Electromagnetic (EM) geophysical methods allow the electrical conductivity of the crust and mantle to be imaged, and this project will use a combination of seismic methods and EM methods to study a magma poor margin southwest of the UK. From this a better understanding of the fundamental tectonic, chemical, and thermal history of continental breakup will be gained. The thermal history is important to the generation of hydrocarbons in this area.The breakup of continents involves a complex interplay of extensional tectonics and magmatism. The final stages of this process, resulting in the initiation of seafloor spreading, remain poorly understood. One common end-member involves hyper-extended continental crust and broad regions of exhumed and serpentinized (hydrated) mantle. Serpentinization at mid-ocean ridges, rifted margins and subduction zones mediates geochemical exchange between the lithosphere and the hydrosphere. There is evidence that normal faulting plays a key role in supplying fluids driving serpentinization beneath hyper-extended continental crust and possibly in regions of exhumed mantle. However, the seismic P-wave velocities of mafic crustal rocks and of serpentinized mantle rocks are similar, so interpretations of seismic data are uncertain. Serpentinized mantle rocks are generally more conductive, often by about an order of magnitude, than mafic crustal rocks, so controlled source electromagnetic (CSEM) and magnetotelluric (MT) techniques provide a promising route to resolve controversies around lithospheric structure. This project will focus on the magma-poor Goban Spur rifted margin to (i) acquire coincident high-quality CSEM, MT, and wide-angle seismic datasets along two carefully chosen transects; (ii) use these data to obtain coincident high-resolution seismic velocity and resistivity models for the upper few kilometers of the lithosphere, and lower-resolution models to tens of kilometers depth; (iii) interpret the resulting models to quantify regional and local variations in mantle serpentinization and magmatic addition; (iv) reconcile these observations with numerical models of lithospheric extension, mantle hydration, and decompression melting as seafloor spreading is initiated.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.